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# What is the chance?

You have fifty coins totaling \$1.00. You drop one down an open drain while tossing the coins in your hand. What is the chance that you have lost a quarter?

There are two ways you can have fifty coins totaling \$1.00; two dimes, forty pennies, and eight nickels; or two dimes, forty-five pennies, two nickels, and one quarter. These arrangements are equally probable, so there is a one­ half chance you had a quarter to begin with. The probability that you then dropped that quarter from all the coins in your hand is one fiftieth. Therefore, the total probability that you lost a quarter is one half times one fiftieth, or one one-hundredth.

## Why?

A woman lives in a skyscraper thirty-six floors high and served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up...

## Explorer

An explorer undertakes to cross a desert with the help of porters. The length of the trail corresponds to 6 days walk. But the explorer, like each porter, can carry only 4 days food. How many porters does the explorer need? In fact, can he cross at all?The...